A man in his 50s was jailed for life last March.
A man has died in Germany, four years after eating a sandwich his colleague had poisoned with mercury.
The 26-year-old had been in a coma since it happened.
A 57-year-old man, identified only as Klaus O. for privacy reasons, was sentenced to life in prison last March after the court found him guilty of attempted murder.
The defendant, who has appealed against the verdict, had peppered co-workers' food with mercury and other substances over several years, leaving one in a coma and two others with serious kidney damage.
Exposure to mercury can cause a number of health issues including skin, neurological and kidney problems.
Most exposure comes from eating fish, coal and gold mining, or dental fillings.
